Terrestrial macroinvertebrates as key elements for sustainable beach management

Recreational activities on sandy beaches are basically human centred and there is little concern of their biological components. Terrestrial sandy shore are often regarded as void boxes of sand to be reconstructed where missing, decorated with coastal vegetation and mechanically cleaned for aesthetic and sanitary reasons. But what costs, in terms of biodiversity loss, are we dealing with? Can beach management be sustainable without considering the fact that terrestrial beach macroinvertebrates are hardly taken into account in management practices? Do beach managers know the importance of terrestrial macroinvertebrates for ecosystem functioning? What measures are needed to avoid the massive loss of species? To address these questions a ten year period of study was conducted on the beach of the Maremma Regional Park (Grosseto, Italy). Here direct impacts due to human activities (beach recreation, trampling, etc) were relatively low, but indirect ones (a severe problem of beach erosion at the Ombrone river mouth) were taking place and large sections of the beach had already been destroyed. Since one of the main attractions of the Maremma Regional Park was the beauty of its beaches (used for summer bathing activities), concerns of the public opinion and of park managers were extremely high. A first approach of our study was to evaluated the health of the beach environment through a baseline ecological study and to pin pointed the main factors causing the erosion process. The study showed that the system was in a dynamic equilibrium with an erosion process going on one side and a accretion process on the other. Biodiversity levels followed linear gradients with increasing levels at increasing distance from the river mouth and were related to increases in habitat complexity. Changes rapidly occurring around the river mouth had produced a shift of the macroinvertebrate community in a buffer area at a higher distance from the river mouth where populations were still consistent in species number and abundance. Furthermore, studying beach populations at increasing distances from the river mouth on a monthly basis demonstrated that terrestrial beach invertebrates (amphipods, isopods, tenebrionids), strictly inhabiting the sand, tended to shift horizontally along the beach to avoid human disturbance according to the season. This finding not only has an ecological importance for the resilience of the ecosystem, showing the value of buffer areas as resources for biodiversity, but also it presents practical aspects as it can be used by beach managers to plan actions for sustainable management. In other beaches where impacts are high this tool could be employed to fine tune spatial and temporal beach cleaning events to avoid further losses of beach species and/or the recovery of others. The study, however, suggests the need of an active interaction between scientists, stakeholders and managers. Communication is also needed between beach ecologists and coastal recreational managers to whom this conference is addressed as more often it has occurred that defence measures have been taken without considering the impacts on the biotic components of the beach ecosystem.